Ram catcher for piston-ram assembly



y 1962 G. E. ATKINSON 3,032,998

RAM CATCHER FOR PISTON-RAM ASSEMBLY Filed May 5, 1961 2 SneetsSheet 1FIG. I

INVENTOR GEORGE E. ATKINSON ATTORNEY y 1962 cs. E. ATKINSON 3,032,998

RAM CATCHER FOR PISTON-RAM ASSEMBLY Filed May 5, 1961 2 Sheets-Sheet 220 FIG. 3

M 22 MENTOR "IIIQ I QQAL l8 GEORGE E. ATKINSON \T Kw BY ZMM%M ATTORNEYUnited States Patent 3,032,998 RAM CATCHER FOR PISTON-RAM ASSEMBLYGeorge E. Atkinson, Linthicum Heights, Md., assignor to The Black andDecker Manufacturing Company, Towson, Md., a corporation of MarylandFiled May 5, 1961, Ser. No. 108,180 11 Claims. (Cl. 60-625) The presentinvention relates to a ram catcher for a piston-ram assembly, and moreparticularly, to such a ram catcher that is actuated upon an initialimpact between the piston and ram, thereby coupling the piston and ramtogether for movement in unison and preventing any further impactingtherebetween.

One specific embodiment, wherein the present invention may findparticular utility, is a portable electric hammer of the type which isprovided with a hollow cylindrical ram having a closed forward end, apiston reciprocating within the ram, a resilient sealing ring carried bythe piston, an entrapped air chamber between the piston and ram, andmomentary venting means to allow the entrapped air to vent at certaintimes during the operating cycle of the tool. The function of theentrapped air is twofold: one, to drive the ram ahead of the piston by acompression of the entrapped air; and two, to retract the ram away fromthe tool bit by means of a suction effect. Thus, the ram willreciprocate in response to, and relatively With respect to, thereciprocating piston; and it will be appreciated that although thevolume of the entrapped air chamber will change during the operatingcycle, still, the sealing eifect of the resilient ring is such as topreclude the piston from bottoming against the ram.

However, at various times at or near the normal life of the tool,usually when the sealing ring has become worn or frayed, the compressionof air in the entrapped air chamber decreases appreciably, with theresult that the piston will bottom against, or initially impact against,the closed forward end of the ram. If this bottoming of the piston withrespect to the ram is allowed to continue, then the physical shocks ofthe repeated impacts will be transmitted, via the piston, to thecross-head, and thence to the connecting rod, gearing, and ultimately tothe motor of the tool; and thus, the basic components of the tool willbe impaired, and quite often, irreparably damaged. Nor can the operatoranticipate or determine the instant of initial bottoming of the piston,inasmuch as the ram will continue to strike a blow against the tool bit,even though the magnitude of the blow is diminished.

Thus the failure of the mere sealing ring will usually be undetected,until serious damage to one or more of the basic components of the toolis encountered; and then, the repair of the tool-will be time-consumingand quite expensive. Moreover, even though the tool may be disconnected,immediately subsequent to failure of the sealing ring and initialbottoming of the piston, nevertheless, prior designs have necessitatedan indirect, and hence expensive, disassembly of the tool in order toreplace the resilient sealing ring.

Accordingly, it is an object of the present invention to provide a ramcatcher for a piston-ram assembly that will alleviate the aforementioneddefects.

It is another object of the present invention to provide a ram catcherfor a piston-ram assembly, which, upon initial bottoming of the piston,will couple the piston and ram together for reciprocation in unison,thus preventing any further bottoming or impacting between the pistonwill be responsive to appreciable wear of the sealing ring to preventrelative movement of the piston and ram.

It is yet still another object of the present invention to provide a ramcatcher, wherein the press-fit acquired between the piston and ram issuflicient to allow the piston and ram to reciprocate in unison, butinsuflicient to preclude the piston and ram from being disengaged by amere manual pulling.

It is a further object of the present invention to provide apower-operated percussive tool having a pistonram assembly and furtherhaving a ram catcher means, wherein, subsequent to actuation of the ramcatcher, the barrel of the tool may be quickly detached, the piston andram separated by a manual pull, and a new sealing ring easily installedon the piston.

In accordance with the teachings of the present invention, there isprovided, in combination, a first member (such as a piston) togetherwith means to reciprocate the first member; and there is furtherprovided a second member (such as a ram) having relative reciprocatingmovement with respect to, and in response to, the first member, achamber being formed between the members for the trapping of acompressive gas therein. Means are further provided to prevent themembers from conv tinually impacting against one another, such meansheing operative after a certain critical amount of gas has leaked fromthe chamber, and comprising a male element and a cooperating femaleelement. Each of these elements are on a respective one of the members,and the elements are normally out of engagement. Thus, when the firstmember initially impacts against the second member, the male and femaleelements acquire a press fit therebetween, thereby coupling the memberstogether for movement in unison and preventing any further impactingbetween the members.

These and other objects of the present invention will become apparentfrom a reading of the following specification, taken in conjunction withthe enclosed drawings, in which:

FIGURE 1 is a longitudinal elevational view of the completepower-operated percussive tool, with parts broken away and sectioned toshow the reciprocating piston, the reciprocating ram, and the ramcatcher means;

FIGURE 2 is an enlarged portion of FIGURE 1, showing the ram catchermeans;

FIGURE 3 shows the piston-ram assembly in its normal function during thelife of the sealing ring;

FIGURE 4 shows the initial bottoming of the piston with respect to theram, the ram catcher means then being actuated to couple the piston andram together;

FIGURE 5 shows the piston and ram coupled together by the ram catcherfor reciprocation in unison, further bottoming of the piston beingprecluded; and

FIGURE 6 is an enlarged portion of a sealing ring that has experiencedappreciable wearing, thus actuating the ram catcher.

With reference to FIGURE 1, there is illustrated a power-operatedpercussive tool, such as a portable electric hammer 10, having a motor11, switch handle 12, gear case 13, connecting rod '14, cross-head 15,piston 16, piston rod 16a, detachable barrel 17, ram 18, tool bit 19,and tool bit retaining means, the latter being denoted generally as at20. Such a hammer, in one specific embodiment thereof, is capable ofdrilling a 2 inch diameter hole, 3 inches deep, in concrete inone-minute; and it will be understood that the percussive shocks andimpacts normally generated, or encountered, by the hammer 10 "are fairlyappreciable.

With reference to FIGURE 2, there is illustrated a relatively-shortdisc-shaped piston 16, which reciprocates within the hollow cylindricalram 18, the space therebetween defining a chamber 21 whereby acompressive gas, such as air, may be entrapped therein. The piston 16has an external annular groove 22, and a suitable resilient sealing ring23 is loosely disposed within the groove 22. Moreover, momentary ventingmeans, hereinafter to be described, is provided so as to allow theentrapped air in chamber 21 to momentarily vent, at certain times,during the operating cycle, thus providing for an equalization of themass of entrapped air in chamber 21 to a substantially constant workinglevel. Hence, as the piston 16 is reciprocated by the cross-head 1S andconnecting rod '14, the entrapped air in chamber 21 will exhibitalternate compression and suction effects, with the result that the ram18 will be reciprocated by a compression of entrapped air in chamber 21to strike a blow upon tool bit 19, and further, that the ram 18 will beretracted from the tool bit 19 by a suction effect created by the rapidwithdrawal of the piston 16 and the consequent sub-atmospheric pressurecreated in the chamber 21; and hence, the ram 18 will be in position foragain being driven by the piston 16 by compression of air in chamber 21,and of course, further striking another blow upon the tool bit 19'. Inno case during the normal life of the tool, however, will'the piston 16strike the ram 18 an actual physical blow, inasmuch as this is precludedby the compression of entrapped air in chamber 2 1, Moreover, at or nearthe normal life of the tool, as when the sealing ring 23 wearsappreciably so as to lose a good sealing effect between the respectivemating walls of the piston 16 and ram 18, the piston 16 will initiallybottom against or impact against the ram 13; and in order to prevent thecontinued bottoming of the piston 16 against the ram 18, a ram catchermeans is provided.

With reference, again, to FIGURE 2, the ram catcher means comprises amale element, such as cylindrical protrusion 24 formed on the forwardface 25 of piston 16, and a cooperating female element, such ascylindrical recess 26, formed in the closed forward end 27 of ram 18 andaligned with protrusion 14. Preferably, but not necessarily, the forwardportion of protrusion 24- is tapered at an angle denoted by X, whichangle X may be in the order of 15, while the depth B of the recess 26 isslightly greater than the height A of the protrusion 24. Thus, when thepiston 16 initially bottoms against the ram 18, the protrusion 24- isreceived within and acquires a press lit with respect to the cooperatingrecess 26, thereby coupling the piston 16 and ram 18 together fornon-relative movement in unison, the purpose of the tapered portion ofprotrusion 24 being to pilot the protrusion 24 within the recess 26.

With reference to FIGURES 3, 4, and 5 the sequential operation of theram catcher means may be more clearly understood. In FIGURE 3, whichrepresents the normal operation of the hammer 10, the piston 16 isreciprocated within the hollow cylindrical ram 18, which, at certaintimes, then strikes a blow against the tool bit 19. In this situation,there is a good sealing of the entrapped air in chamber 21, and the ramcatcher means is, in a sense, dormant. At or near the normal life of thehammer 10 say the normal life of the sealing ring 23 (whichincidentally, is usually in the order of at least several hundred hours)the piston 16 will initially bottom against the ram 18; and the ramcatcher means is, in a sense, actuated to create a physical couplingbetween the piston 16 and ram 18, as shown in FIGURE 4. Naturally, itwill be understood by those skilled in the art that the axial positionof the piston 16 and ram 18 (with respect to barrel 17) at the instantof lock up of the piston 16 and ram 18, may vary and that the positionshown in FIGURE 4 is only a typical illustration. Moreover, it will befurther understood that the teachings of the present invention areequally applicable to other forms of piston-ram assemblies, and that theparticular form of piston 16 and ram 18, herein illustrated, representsa typical embodiment of the present invention.

It will be further appreciated that, in the usual operation of thehammer 10, that the piston 16 and ram 18 reciprocate relatively to eachother, that is to say, the

piston 16 and ram 18 do not ordinarily reciprocate in unison with eachother; and there is a portion in the operating cycle of the mechanismwhere in the piston 16 is being driven forwardly (by means of theconnecting rod 14 and cross-head 15) at the very instant when the ram 18is still being retracted rearwardly by the suction effect previouslyexhibited by the retracting piston 16. Moreover, there is a point duringthe normal operating cycle wherein the piston 16 and ram 18 are fairlyclose to each other, although not physically contacting one another.Then, as the sealing ring 23 wears appreciably over the life of thehammer 10, the alternate compression and suction etfects exhibited bythe entrapped air in chamber 21 will diminish, but nevertheless, thereis still a residual or modicum of suction effect sufiicient to cause theram 18 to be retracted somewhat, and that, in combination with thenormal rebound of the ram 18 from striking the tool bit 19, causes theram '18 to be retracted sufiiciently to physically engage the movingpiston 16; and the initial physical contact of the piston 16 and ram 18will actuate the ram catcher means, in the manner hereinbeforeexplained. Thereafter, the piston 16 and ram 18 will no longer moverelatively with respect to each other, but rather, will now reciprocatein unison, preventing any further bottoming of the piston 16 withrespect to the ram 18, and preventing any further striking of the ram 18against the tool bit 19. In an actual test of the teachings of thepresent invention, a new sealing ring 23 was deliberately ground downand then installed in the hammer 1d; and as soon as the hammer 10 wasactuated, the ram catcher means of the present invention caused thepiston 16 to immediately engage and hold the ram 18 without anycontinuous bottoming or impacting therebetween.

Thus, when the ram catcher means is actuated, the piston 16 and ram 18will reciprocate together, in unison, so as to preclude any further andrepeated bottoming or impacting therebetween; and naturally, the ram 18is preeluded from impacting against the tool bit 19. Hence, no repeatedblows are developed by the hammer 10, and no harmful repeated impactsare related or transmitted back to the major components of the hammer11); and the operator is automatically informed of the failure of thesealing ring 23 and the consequent actuation of the ram catcher means,inasmuch as the ram 18 is precluded from impacting against the tool bit19, and inasmuch as the weight of the ram 18 added to the piston 16creates a noticeable unbalance in the hammer 10. A typical case ofappreciable wear of the sealing ring 23 is illustrated in FIGURE 6,wherein theclearance between the mating walls of the piston 16 and ram18 is deliberately exaggerated for purposes of illustration. Sealingring 23 is of the resilient type, but of course, it is understood thatthe present invention may be practiced with various forms of sealingrings made of various materials. Also, in FIGURES 3, 4, and 5, sealingring 23 is illustrated as being in the forward portion of groove 22 onpiston 16, as when the piston 16 is moving rearwardly; naturally, itwill be appreciated that when piston 16 is moving forwardly of barrel17, that the sealing ring 23 will probably be in the rearward portion ofgroove 22. However, in

the drawings, the sealing ring 23 is illustrated in the forward portionof groove 22 for sake of convenience.

Once the ram catcher means has thus been actuated, the operator may theneasily disassemble the barrel 17 from the hammer 10 by removing aplurality of mounting screws 28 (shown in FIGURE 1) between the barrel17 and gear case 13; and thereafter the ram 18 may be removed from thepiston 16 by a manual pulling, it being recalled that the press fitacquired between protrusion 24 and recess 26 is sufficient to precluderelative movement of the piston 16 and ram 18, but insufficient topreclude a separation by. a normal manual pulling, and especially, by acombined pulling and twisting that may be exerted to a substantiallyconstant working level.

' pairment, even if and when the sealing ring 23 fails; and imoreover,the operator is instantly informed of the failure of the sealing ring23, and the replacement of the sealing ring 23 is simple, easy, anddirect.

The momentary venting means (hereinbefore mentioned) for the entrappedair in chamber 21, comprises the relatively-short disc-shaped piston 16in combination with an internal annular recess 29 in the ram 18, whereinthe axial width of the recess 29 is greater than the axial height of thepiston 16. Therefore, the entrapped air in chamber 21 is allowed tovent, at certain times during the operating cycle of the mechanism (aswhen the piston 16 passes by the recess 29), thus enabling the entrappedair to compensate for slight, but inherent, leakages in the mechanism,and thus enabling the entrapped air to adjust Such momentary ventingmeans is described more particularly in the co-pending Akermanapplication S.N. 18,178 filed March :28, 1960, and assigned to the sameassignee as the present invention. However, it will be appreciated thatthe present invention may be practiced with various forms of ventin'g"means.

Obviously, many modifications may be made without departing from thebasic spirit of the present invention; and therefore, within the scopeof the appended claims, the invention may be practiced other than hasbeen specifically described.

I claim:

1. In combination, a first member, means to reciprocate said firstmember, a second member having relative reciprocating movement withrespect to and in response to said first member, a chamber between saidmembers, whereby a compressive gas may be trapped therein, and means toprevent said members from continually impacting against each other, saidmeans being operative after a certain critical amount of gas has leakedfrom said chamber and comprising a male element and a cooperating femaleelement, each of said elements on a respective one of said members, saidelements being normally out of engagement, whereby when said firstmember initially impacts against said second member, said male andfemale elements will acquire a press fit therebetween, thereby couplingsaid members together for movement in unison and preventing any furtherimpacting between said members.

2.. In combination, a reciprocating piston, a reciprocating ram havingrelative movement with respect to and in response to said piston, achamber between said piston and said ram, whereby a compressive gas maybe trapped therein, and means to prevent said piston from continuallybottoming against said ram, said means comprising a protrusion formed onsaid piston, and said ram having a cooperating recess, said protrusionand said recess being normally out of engagement, whereby when asuificient quantity of said compressive gas leaks from said chamber andsaid piston initially bottoms against said ram, said protrusion willacquire a press fit with respect to said recess, thereby coupling saidpiston and ram together for movement in unison and preventing anyfurther bottoming of said ram and piston.

3. In combination, a cylindrical ram having a blind axial bore, acylindrical piston telescoped within said ram, said piston and said ramhaving a chamber therebetween, whereby air may be trapped therein,poweroperated means to reciprocate said piston, whereby said ram willreciprocate relatively with respect to and in response to said piston,momentary venting means for the entrapped air in said chamber, and meansto prevent said when said piston initially bottoms against said ram,said piston from continually bottoming against said ram, said meansbeing operative after a certain critical mass of air has leaked fromsaid chamber and comprising a protrusion formed on said piston, and saidram having a cooperating recess, said protrusion and said recess beingnormally out of engagement, whereby when said piston initially bottomsagainst said ram, said protrusion and said recess will acquire a pressfit therebetween, thereby coupling said piston and ram together fornon-relative movement in unison and preventing any further impactingbetween said piston and ram.

4. In a percussive tool, the combination of a hollow cylindrical ramhaving a closed forward end including an interior wall transverse to theaxis of said cylindrical ram, a disc-shaped relatively-short pistontelescoped within said ram and having a flat forward face parallel tosaid interior wall of said ram, said wall and said face and the walls ofsaid cylindrical ram forming a cylindrical chamber therebetween, wherebyair may be trapped therein, power-operated means to reciprocate saidpiston,

means for the entrapped air in said chamber, and means to prevent saidpiston from continually bottoming against said ram, said means beingoperative after a certain critical mass of air has leaked from saidchamber and comprising a protrusion projecting from said forward face ofsaid piston, and said ram having a cooperating aligned recess in saidinterior wall thereof, said protrusion and said recess being normallyout of engagement, whereby protrusion and said recess will acquire apress fit therebetween, thereby coupling said piston and ram togetherfor non-relative movement in unison and preventing any further impactingbetween said piston and ram.

5. The combination according to claim 4, wherein said protrusion andsaid recess are cylindrically-formed and are aligned with the axis ofsaid cylindrical ram.

6. The combination according to claim 5, wherein said recess has anaxial length which is slightly greater than the axial length of saidprotrusion.

7. The combination according to claim 5, wherein said protrusion has abeveled forward portion to pilot said protrusion in said recess.

8. In a percussive tool, the combination of a hollow cylindricalfloating ram having a closed forward end, a piston telescoped forreciprocation within said ram, a sealing ring carried by said piston,means to reciprocate said piston, a chamber between said piston and ram,whereby air may be trapped in said chamber, and whereby the alternatecompression and suction efiects of the entrapped air in said chamberwill cause said ram to reciprocate relatively with respect to saidpiston, momentary venting means for the entrapped air in said chamber,and means to prevent relative movement of said piston and ram, saidmeans being responsive to appreciable wear of said sealing ring and theconsequent loss of compression in said chamber and comprising a pair ofelements, one on said piston and the other on said ram, said elementsbeing physically coupled together upon the physical engagement of saidpiston with said ram, whereby said piston and said ram will thereafterreciprocate in unison.

9. The combination according to claim 8, wherein said responsive meanscauses said elements to acquire a press fit therebetween, said fit beingsuflicient to prevent relative movement between said piston and ram inthe percussive tool, but insufficient to prevent said piston and ramfrom being manually pulled apart.

It). A power-operated percussive tool comprising a motor housing, amotor in said motor housing, a gear case secured to said motor housing,a longitudinal barrel having a cylindrical bore, means to detachablysecure said barrel forwardly of gear case, a cross-head reciprocating insaid bore of said barrel, motion-translating means in said gear case andcoupled between said cross-head and said IIIOtOIyB. cylindrical ramguided for reciprocation in said here of said barrel, 'said ram having ablind axial bore, a disc-shaped piston telescoped within said ram, a

sealing ring carried by said piston, a piston rod between entrapped airin said chamber Will exhibit alternate compression and suction efiects,thereby reciprocating said ram relatively to said piston, said barrelhaving a forward portion, a tool bit disposed in said forward portion ofsaid barrel, retaining means for said tool bit, whereby said ram willdeliver a 'blow against said tool bit, a protrusion formed on saidpiston, and said ram having a cooperating recess, whereby as saidsealing ring wears appreciably and the alternate compression and suctioneifects of the entrapped air in said chamber become insuflicient toreciprocate said ram, said piston will initially bottom against saidram, thereby causing said protrusion to acquire a press fit withrespectto said recess to mechanically couple said ram to said piston,and whereby said piston and ram will thereafter reciprocate in unisonand said ram will be precluded'from thereafter delivering a blow againstsaid'tool bit.

ll. A power-operated percussive tool comprising a motor housing, a motorin said motor housing, a gear case secnredto said motor housing, alongitudinal barrel having a cylindrical bore, means to detachablysecure said barrel forwardly of said gear case, a cross#headreciprocating in said bore of said barrel, motion-translatingm'eans'insaid ,gear case and coupled between said crosshead and saidmotor, a cylindrical ram guided for reciprocation in said bore of saidbarrel, saidtram having a blind axial bore, a disc-shapedpistontelescoped Within said ram, a sealing ring carried by said piston, apiston rod between said piston and cross-head, a chamber between saidram and said piston, whereby air may be entrapped in said chamber,momentary venting meansfor the entrapped air in said chamber, whereby assaid piston reciprocates, the entrapped air in said chamber will exhibitalternate compression and suction effects, thereby reciprocating saidram relatively to said :piston, said barrel having a forward portion, atool bit disposed in said forward portion of said barrel, retainingmeans for said tool bit, whereby said ram will deliver a blow againstsaid tool bit, means to prevent said piston from continually bottomingagainst said ram, said means being responsive to appreciable wear ofsaid sealing ring and the consequent loss of compression in said chamberand comprising a pair of elements, one on said piston and the other onsaid ram, said elements acquiring a press fit therebetween upon thebottoming of said piston with respect to said ram, said piston and saidram thereafter reciprocating in unison and said ram being precluded fromdelivering a blow against said tool bit, and said press fit between saidelements being insufficient to preclude a manual disengagement of saidpiston and said ram, whereby said barrel may be detached from saidlgear'case, and whereby said ram may be manually disengaged from saidpiston, thereby allowing a replacement of said sealing ring.

References Cited in the file of this patent UNITED STATES PATENTS2,880,585 Badcock Apr. 7, 1959

